ELECTRIC RESPONSES TO COLOR SHIFT IN FROG AND TURTLE RETINA

Abstract

Onset and cessation of illumination both evoke electric responses in vertebrate retinas. If with no change in effective intensity, shift from one color to another evokes electric response, it relates the source of potential to color discrimination. A beam-splitter brought 2 light beams to coincidence on the retinas of frogs or turtles. Interference filters delivered nearly monochromatic light,- red, yellow, green or blue. A beam-shifting shutter made the transition between colors with minimum flicker. Intensities were balanced with rheostats in the lamp circuits. With all 6 combinations of these colors the shift evoked electric responses; no balancing of intensities abolished it. The form of response in long wave to short wave shift differed from that in the reverse shift. In dark-adapted frogs, when the beams were equivalent as judged by the [image][image]-wave[image] (positive), the preceding [image][image]a-wave[image] (negative) was absent or small and brief in the short-to-longwave shift, larger in the reverse shift. The [image]-wave showed longer duration in short-to-long-wave shift than in the reverse. Frogs have both rods and cones; the above differences might relate to differential involvement of rods and cones in response to different colors. Yellow and blue with light-adapted frogs showed reversal of the above differences. Turtle retinas (only cones) showed shift responses with less difference between short-to-long and long-to-short shifts than in the frog. The slight differences more nearly resembled those in light-adapted than in dark-adapted frogs. Rod-cone differential may therefore explain some but not all features of the responses.